Biofouling was discovered to clog the membrane structure and feed channel so that little to no power was generated.

SEDE BOQER, Israel — Dec. 28, 2015 — A recent study found that because of biofouling, pressure-retarded osmosis (PRO) technology is not feasible, according to a press release.

Biofouling occurs when organic material and organisms such as algae and bacteria accumulate on surfaces, impairing structures and hindering system performance, stated the release.

PRO has been regarded over the last few decades as having potential to provide a sustainable energy source, reported the release. “It utilizes various salinity gradients, such as sea and river water, or desalination brine and wastewater. In PRO, water from a low-salinity feed solution permeates through a membrane into a pressurized, high-salinity draw solution. Power is obtained by depressurizing the draw through a hydroturbine.”

Researchers from the Zuckerberg Institute for Water Research at Ben-Gurion University of the Negev published their findings in the journal Environmental Science & Technology, noted the release. Because of biofouling, they wrote, the membrane structure and feed channel were so clogged that PRO produced almost no power generation. Yale University researchers reported in an earlier study that PRO is thermodynamically challenging and nearly unviable.

“While the concept of using an ‘osmotic gradient’ to harness power has existed since the 1970s, our research shows that commercial PRO is currently ‘dead in the water,’” said Zuckerberg’s Dr. Edo Bar-Zeev in the release. “Biofouling is detrimental to the process and can’t be mitigated since there are no membranes today that are specifically designed for PRO.”

Zeev noted that either sterile streams or a new membrane design are necessary for the process to be viable, shared the release. “These membranes must be dedicated for PRO technology instead of using the current forward osmosis (FO) membranes.”

The researchers used synthetic wastewater secondary effluents and seawater reverse osmosis desalination brine in the study, stated the release. Experiments were conducted in a small-scale PRO setup with thin-film composite FO membrane and fabric feed spacers.

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